1. Field of the Invention
The present invention is generally related to a marine transmission, or gear shifting mechanism, and more particularly to a two-speed transmission control strategy that selects the appropriate gear ratio based solely on engine speed, as represented by engine crankshaft RPM and the rate of change of the engine crankshaft RPM.
2. Description of the Prior Art
Multi-speed marine propulsion systems have been developed to provide the ability to change the ratio of speed between the crankshaft of an engine and the propeller shaft of a marine vessel. Control strategies for selecting a gear ratio of the transmission have typically been based on several input parameters, such as manifold absolute pressure (MAP), load on the system, throttle position, and speed.
U.S. Pat. No. 5,711,742, which issued to Leinonen et al on Jan. 27, 1998, describes a multi-speed marine propulsion system with automatic shifting mechanism. The system, preferably having dual counterrotating propellers, has an automatic multi-speed shifting mechanism such as a transmission. An electronic controller monitors engine parameters such as engine revolution speed and load, and generates a control signal in response thereto, which is used to control shifting. Engine load is preferably monitored by sensing engine manifold air pressure. The electronic controller preferably has a shift parameter matrix stored within a programmable memory for comparing engine speed and engine load data to generate the control signal. The system can also have a manual override switch to override shifting of the shifting mechanism.
U.S. Pat. No. 4,820,209, which issued to Newman on Apr. 11, 1989, describes a torque converter marine transmission with a variable power output. A fluid coupling is provided in a marine drive between the engine and the propulsion unit. The fluid coupling includes a fluid pump adapted to be driven by the crankshaft of the engine, and a turbine adapted to be driven by the fuel pump. A series of reactor veins is provided in the fluid coupling. The reactor veins are adapted to be driven in a direction opposite the direction of rotation of the fluid pump. The turbine and the reactor veins are connected to shafts which extend from the fluid coupling to a transmission housing. Each shaft is provided with a gear and a brake disc. An output shaft extends from the transmission housing, and includes a pair of freely rotatable gears engageable with the gears on the reactor shaft and the turbine shaft. Clutch mechanisms are provided on the freely rotatable output shaft gears for selectively engaged the reactor shaft gear in the turbine shaft gear to provide rotation of the output shaft in response to rotation of the reactor shaft and turbine shaft gears. A variable force brake is applied to a disc connected to the output shaft to govern the amount of power transferred by the output shaft to the propulsion unit. The variable force brake is selectively actuable to govern the output of the fluid coupling during low speed operation to provide increased boat performance at such speeds.
U.S. Pat. No. 5,018,996, which issued to Newman et al on May 28, 1991, discloses a flow control fluid coupling marine transmission. A fluid coupling transmission is adapted for interposition between the engine and the propulsion unit of a marine drive. The fluid coupling transmission provides variable speed operation in both forward and reverse. A fluid pump is drivingly connected to the engine crankshaft, and is adapted to drive a turbine. A series of variable position vanes are disposed between the fluid pump and turbine at the entrance of fluid into the pump, for controlling the power transfer therebetween by controlling the amount of fluid passing through the pump and acting on the turbine. A ring gear is connected to the turbine, and a sun gear is connected to the output shaft of the transmission. One or more planet gears are provided between the ring gear and the sun gear, and are rotatably mounted to a carrier member, which extends coaxially with respect to the output shaft. An output control mechanism, including a brake band and a plate clutch mechanism, is selectively engagable with the carrier member so as to control the direction of rotation of the transmission output shaft.
U.S. Pat. No. 5,738,605, which issued to Fliearman et al on Apr. 14, 1998, describes an anti-hunt strategy for an automatic transmission. An anti-hunt transmission control strategy for controlling an automatic transmission so as to prevent the occurrence of a shift hunting condition is provided. The control strategy determines a learned vehicle inertia as well as road load torque and expected torque in an upshift gear. A projected post shift acceleration is predicted based on the expected torque, road load torque and inertia of the vehicle. If vehicle speed and throttle position are within an allowable shift zone and if the predicted post shift acceleration exceeds a threshold value, the vehicle automatic transmission is allowed to upshift. Otherwise, should the predicted post shift acceleration not exceed the threshold value, an upshift is prevented.
U.S. Pat. No. 5,419,412, which issued to Schwab et al on May 30, 1995, describes a gear-shift control and gear-range selector for a semi automatic or fully automatic motion vehicle gearbox. In a motor vehicle having a transmission which can be optionally operated fully automatically or semi-automatically, and in which a gear-range selector and a gear-shift control are provided, the gear-shift control is applicable. The gear-range selector makes it possible to preselect a travel speed in which the transmission is gradually shifted up or down by actuating the gear-shift control. The gear-shift control is designed as a foot switch located in the foot area of a driver's cab of a motor vehicle, so that both of the driver's hand can stay on the steering wheel while these gear-shift operations are being carried out thereby permitting the driver to concentrate fully on the traffic.
The above described United States patents are hereby explicitly incorporated by reference in the description of the present invention.
It would be significantly beneficial if a simplified gear shifting algorithm, or strategy could be provided in which shifting from one gear ratio to another gear ratio is determined solely as a function of the operating speed of an engine, as represented by the crankshaft rotational speed, in RPM, and the rate of change of the crankshaft rotation speed in RPM per second squared.